Fault detection systems and methods for self-optimizing heating, ventilation, and air conditioning controls

ABSTRACT

A fault detection system for detecting a fault in a process system includes a first circuit configured to modify an input of the process system with a modifying signal. The fault detection system further includes a second circuit configured to receive an output from the process system and configured to determine whether the fault exists based on at least one of a reduction of a signal component and an unexpected transformation of the signal component, wherein the signal component corresponds to a function of the modifying signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.12/323,293, filed Nov. 25, 2008, which is a continuation-in-part ofInternational Application No. PCT/US2008/070091, filed Jul. 15, 2008,which claims the benefit of U.S. Provisional Application No. 60/950,314,filed Jul. 17, 2007. The entire contents of U.S. application Ser. No.12/323,293, PCT Application No. PCT/US2008/070091 and U.S. ProvisionalApplication No. 60/950,314 are hereby incorporated by reference.

BACKGROUND

The present application relates generally to the field of heating,ventilation, and air conditioning (HVAC) control. More specifically, thepresent application relates to fault detection systems and methods forself-optimizing HVAC control.

Self-optimizing control strategies are used in the field of HVAC controlto optimize the performance of one or more HVAC control loops. Forexample, in an air-side economizer application, a damper driven by aself-optimizing control strategy is used to minimize the energyconsumption of an air handling unit (AHU) by using cool outside air tocool an indoor space (e.g., when conditioning outside air is more energyefficient than cooling and conditioning recirculated air).

Component malfunctioning in self-optimized control loops can present anumber of problems. For example, a faulty component utilized in aself-optimized control loop can impair functionality and lead to energywaste rather than energy savings. More particularly, in the air-sideeconomizer example, damper malfunctioning prevents acceptable airhandling unit (AHU) operation. Damper faults include failed actuator,damper obstruction, de-coupled linkage, and other errors.

What is needed is a system and method for detecting faults in HVACsystems using self-optimizing control strategies.

SUMMARY

One embodiment of the invention relates to a method for detecting afault in a process system. The method includes modifying an input of theprocess system with a modifying signal. The method also includesmonitoring an output of the process system for a signal componentcorresponding to a function of the modifying signal and determining thatthe fault exists based on at least one of a reduction of the signalcomponent and an unexpected transformation of the signal component.

Another embodiment of the invention relates to a fault detection systemfor detecting a fault in a process system. The fault detection systemincludes a first circuit configured to modify an input of the processsystem with a modifying signal. The fault detection system furtherincludes a second circuit configured to receive an output from theprocess system and configured to determine whether the fault existsbased on at least one of a reduction of a signal component and anunexpected transformation of the signal component, wherein the signalcomponent corresponds to a function of the modifying signal.

Another embodiment of the invention relates to a controller fordetecting a fault in a process system. The controller includes a circuitconfigured to affect an input of the process system, the circuitconfigured to modify the input with a modifying signal, wherein thecircuit is further configured to monitor an output of the process systemfor a signal component corresponding to a function of the modifyingsignal, and wherein the circuit is further configured to determinewhether the fault exists based on at least one of a reduction of thesignal component and an unexpected transformation of the signalcomponent.

Alternative exemplary embodiments relate to other features andcombinations of features as may be generally recited in the claims.

BRIEF DESCRIPTION OF THE FIGURES

The disclosure will become more fully understood from the followingdetailed description, taking in conjunction with the accompanyingfigures, wherein like reference numerals refer to like elements, inwhich:

FIG. 1 is a perspective view of a building with an HVAC system having anAHU, according to an exemplary embodiment;

FIG. 2 is a schematic diagram of an HVAC system having an AHU, accordingto an exemplary embodiment;

FIG. 3 is a flow chart of a finite state machine of the HVAC system ofFIG. 2, according to an exemplary embodiment;

FIG. 4 is a diagram of a system for operating and optimizing a processsystem, according to an exemplary embodiment;

FIG. 5A is a diagram of the system of FIG. 4 with additional elementsfor detecting a fault in the process system, according to an exemplaryembodiment;

FIG. 5B is a diagram of the system of FIG. 4 with additional elementsfor detecting a fault in the process system, according to anotherexemplary embodiment;

FIG. 6A is a diagram of the system of FIG. 4 with additional elementsfor detecting a fault in the process system, according to yet anotherexemplary embodiment;

FIG. 6B is a diagram of the system of FIG. 4 with additional elementsfor detecting a fault in the process system, according to yet anotherexemplary embodiment;

FIG. 7 is a diagram of a control system for an AHU, according to anexemplary embodiment;

FIG. 8 is a detailed diagram of a system for operating and optimizing aprocess system and with additional elements for detecting a fault in theprocess system, according to an exemplary embodiment;

FIG. 9 is a diagram of an self-optimizing system that utilizes anextremum seeking controller with actuator saturation control, accordingto an exemplary embodiment;

FIG. 10 is a diagram of a system configured to utilize multi-variableextremum seeking control output for fault detection of the system,according to an exemplary embodiment;

FIG. 11 is a diagram of a system configured to utilize multi-variableextremum seeking control output for fault detection of the system,according to another exemplary embodiment;

FIG. 12 is a flow chart of a process for detecting a fault in a processsystem, according to an exemplary embodiment;

FIG. 13 is a flow chart of a process for detecting a fault in a processsystem, according to another exemplary embodiment; and

FIG. 14 is a block diagram of a control system for affecting thetemperature of a building space, according to an exemplary embodiment.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Before turning to the figures which illustrate the exemplary embodimentsin detail, it should be understood that the application is not limitedto the details or methodology set forth in the description orillustrated in the figures. It should also be understood that theterminology is for the purpose of description only and should not beregarded as limiting.

Referring generally to the figures, systems and methods for detectingfaults in a self-optimizing control system are shown. A modified signalis applied to an input of a process system and an output of the processsystem is monitored for a signal component that is a function of themodified input signal. A fault is determined to exist based on areduction of the signal component or an unexpected transformation of thesignal component. Some of the embodiments described relate specificallyto the use of a fault detection circuit with an extremum seekingcontroller. Perturbed inputs of the process system provided by theextremum seeking controller can be used for optimization purposes andfor fault detection purposes, with the system determining that a faultexists when the perturbed input does not result in an expected and/orcorresponding output. In the HVAC context, and particularly in theair-side economizer context, a self-optimizing control strategy used toadjust a damper that affects the outside air provided to an AHU can bemonitored for faults by checking for the existence of an expected signalcomponent at an output of the self-optimizing control strategy (e.g., byexamining a performance measure of the process system used by theself-optimizing control strategy).

FIG. 1 is a perspective view of a building 2 with an HVAC system,according to an exemplary embodiment. As illustrated, building 2includes an AHU 4 that is part of an HVAC system that is used tocondition, chill, heat, and/or control the environment of an interiorarea 6 of building 2. The control system for AHU 4 is configured toutilize an extremum seeking control (ESC) strategy to provide economizerfunctionality; optimizing the flow of air provided to AHU 4 from theoutside in order to minimize the power consumption of AHU 4.

ESC is a class of self-optimizing control strategies that candynamically search for inputs of an unknown and/or time-varying systemto optimize performance of the system. One application for ESC is toprovide economizer control to an AHU, seeking to optimize the behaviorof a damper controlled by an actuator to minimize the power consumptionof the AHU. ESC can also be used for other applications inside andoutside the HVAC industry (e.g., wind turbine control, fluid pumpcontrol, energy delivery control, etc.). In an ESC strategy, a gradientof process system output with respect to process system input istypically obtained by slightly perturbing the operation of the systemand applying a demodulation measure. Optimization of process systemperformance is obtained by driving the gradient towards zero by using anintegrator or another mechanism for reducing the gradient in aclosed-loop system.

According to other exemplary embodiments, building 2 may contain moreAHUs. Each AHU may be assigned a zone (e.g., area 6, a set of areas, aroom, part of a room, a floor, a part of a floor, etc.) of building 2that the AHU is configured to affect (e.g., condition, cool, heat,ventilate, etc.). Each zone assigned to an AHU may be further subdividedthrough the use of variable air volume boxes or other HVACconfigurations.

While the present application describes the invention with frequentreference to the application of air-side economizers in HVAC systems,the present invention may be utilized with applications andself-optimizing control loops other than those described herein.

Referring now to FIG. 2, a schematic diagram of an environmental controlsystem 200 (e.g., HVAC control system) having an AHU 4 is shown,according to an exemplary embodiment. Environmental control system 200includes a workstation 202, a supervisory controller 204 (e.g., anetwork automation engine (NAE)), and an AHU controller 210. Accordingto an exemplary embodiment, AHU controller 210 is configured to utilizean ESC strategy. AHU controller 210 is coupled to supervisory controller204 via communications link 220. Workstation 202 and supervisorycontroller 204 are coupled via a communications bus 206. Communicationsbus 206 may be coupled to additional sections or additional controllers,as well as other components utilized in environmental control system200. Environmental control system 200 may be a building automationsystem such as a METASYS® brand system manufactured by Johnson Controls,Inc.

Referring now to FIGS. 2 and 3, controller 210 is operatively associatedwith AHU 4 and controller 210 is configured to operate as a finite statemachine with the three states depicted in FIG. 3, according to anexemplary embodiment. Controller 210 operates AHU 4 using ESC when instate 303. A transition occurs from one state to another, as indicatedby the arrows, when a specified condition or set of conditions occurs.In an exemplary embodiment, operation data of AHU 4 is checked whencontroller 210 is in a given state to determine whether a transitioncondition exists. A transition condition may be a function of thepresent state of the system, a specific time interval, a temperaturecondition, a supply air condition, a return air condition and/or otherconditions that may exist and be utilized by controller 210.

In cold climates, the initial state of control is heating in state 301.The system starts up in state 301 to minimize the potential that coolingcoil 244 and/or heating coil 240 will freeze. In state 301, valve 242for heating coil 240 is controlled to modulate the flow of hot water,steam, or electricity to heating coil 240, thereby controlling theamount of energy transferred to the air in an effort to maintain thesupply air temperature at the setpoint. Dampers 260, 262, and 264 arepositioned for a minimum flow rate of outdoor air and there is nomechanical cooling, (i.e., chilled water valve 246 is closed). Theminimum flow rate of outdoor air is the least amount required forsatisfactory ventilation to the supply duct 290. For example, 20% of theair supplied to duct 290 is outdoor air. The condition for a transitionto state 302 from state 301 is defined by the heating control signalremaining in the “No Heat Mode.” Such a mode occurs when valve 242 ofheating coil 240 remains closed for a fixed period of time (i.e.,heating of the supply air is not required during that period). Thistransition condition can result from the outdoor temperature rising to apoint at which the air from supply duct 290 does not need mechanicalheating or after the heating control signal has been at its minimumvalue (no-heat position) for a fixed period of time.

In state 302, the system is utilizing outdoor air to provide freecooling to the system. State 302 controls the supply air temperature bymodulating dampers 260, 262, and 264 to adjust the mixing of outdoor airwith return air (i.e., no mechanical heating or cooling). The amount ofoutdoor air that is mixed with the return air from return duct 292 isregulated to heat or cool the air being supplied via supply duct 290.Because there is no heating or mechanical cooling, the inability toachieve the setpoint temperature results in a transition to either state301 or state 303. A transition occurs to state 301 for mechanicalheating when either for a fixed period of time the flow of outdoor airis less than that required for proper ventilation or outdoor air inletdamper 262 remains in the minimum open position for a given period oftime. The finite state machine makes a transition from state 302 tostate 303 for mechanical cooling upon the damper control remaining inthe maximum outdoor air position (e.g., 100% of the air supplied by theAHU is outdoor air) for a fixed period of time.

In state 303, chilled water valve 246 for cooling coil 244 is controlledto modulate the flow of chilled water and to control the amount ofenergy removed from the air. Further, ESC is used to modulate dampers260, 262, and 264 to introduce an optimal amount of outdoor air into AHU4. In an exemplary embodiment, a transition occurs to state 302 when themechanical cooling does not occur for the fixed period of time (i.e.,the cooling control is saturated in the no-cooling mode).

Referring now to FIG. 4, a simplified block diagram of a system 400 foroperating and optimizing a process system 404 is shown, according to anexemplary embodiment. According to various exemplary embodiments, aprocess system is any electronic or mechanical system (one more hardwaredevices) that uses one or more input signals to controllably affect oneor more output signals. The process system, for example, may be an airhandling unit that uses setpoint and/or position inputs to affect one ormore properties of air. According to other exemplary embodiments, theprocess system may be an energy conversion system (e.g., a wind turbinesystem, a photovoltaic system, a hydraulic energy conversion system,etc.), a hydraulic system, a pumping system, or the like that can becontrolled for desirable performance.

System 400 is shown to include a controller 402 (e.g., a localcontroller, a feedback controller) that provides an input (e.g., anactuating input) to process system 404. The input may be provided toprocess system 404 as a function of a setpoint (or other inputs)received by controller 402. Extremum seeking controller 406 receives oneor more outputs (e.g., a performance measure) from process system 404and provides an optimizing input to process system 404 to optimize theprocess system's behavior (e.g., to optimize energy consumption, etc.).

Referring now to FIG. 5A, the diagram of FIG. 4 is shown with additionalelements for detecting a fault in process system 404, according to anexemplary embodiment. Particularly, system 500 is shown to includemodifying signal generator 407 and fault detection module 408. Modifyingsignal generator 407 is configured to modify an input of process system404 with a modifying signal. Fault detection module 408 is configured tomonitor an output of process system 404 for a signal componentcorresponding to a function of the modifying signal. Fault detectionmodule 408 determines that process system 404 is fault free if thesignal component is available. In other words, fault detection module408 determines that process system 404 includes a fault based on atleast one of a reduction of the signal component and an unexpectedtransformation of the signal component relative to the modifying signal.

As shown in FIG. 5A, the input modified is the input to process system404 provided by extremum seeking controller 406. It should be noted thatthe modifying signal that modifies an input of process system 404 couldbe added to the system by extremum seeking controller 406. For example,a normal perturbation of the extremum seeking controller may be themodifying signal provided to the system.

It might be noted that, in various exemplary embodiments, the inputmodified for the purpose of fault detection may be other than anoptimizing input. For example, FIG. 5B illustrates an embodiment inwhich signal generator 409 modifies an input provided to process system404 from feedback controller 402.

Referring still to FIG. 5A, the output monitored by fault detectionmodule 408 is a performance measure utilized in the control loop ofextremum seeking controller 406. By contrast, system 600 of FIG. 6Aillustrates fault detection module 608 receiving an output from processsystem 604 that is not fed back to extremum seeking controller 606. Inthe embodiment shown in FIG. 6A, extremum seeking controller 606provides the modifying signal to an input of process system 604 withoutthe assistance of a separate signal generator (e.g., modifying signalgenerator 407 as shown in FIG. 5A-B). In decision block 610 of faultdetection module 608, an output from process system 604 is monitored forthe periodic component of the modifying signal at 2π/T, where T is theperiod of the modifying input. In other words, fault detection module608 monitors for the periodic component of the modifying input at theangular frequency of the modifying signal.

It might be noted that, in various exemplary embodiments, any one ormore outputs from the process system may be used by the fault detectionmodule to monitor for the modifying input. For example, in system 650 ofFIG. 6B, fault detection module 608 is shown receiving an output fromprocess system 605 that is not provided back to either extremum seekingcontroller 606 or feedback controller 601. In various embodiments, theoutput monitored by the fault detection module may be generated by theprocess system itself, by one or more sensors utilized by the extremumseeking controller, the process system and/or by the feedbackcontroller, or the output monitored by the fault detection module may begenerated by a sensor not otherwise used by the system or used by acomponent remote from the system.

Referring now to FIG. 7, a control system 700 for AHU 716 is shown,according to an exemplary embodiment. In control system 700, extremumseeking controller 706 provides a signal that controls the position of adamper associated with AHU 716. Feedback controller 702 provides acooling coil value position, or another value, to control to AHU 716 andto extremum seeking controller 706. Feedback controller 702 determinesthe cooling coil setpoint based on a temperature setpoint received froma controller (e.g., a supervisory controller, an enterprise levelcontroller, a field controller, a user interface, etc.) upstream ofcontroller 702. According to an exemplary embodiment, the damperposition is modulated in a manner that is calculated to cause expectedperturbations in the supply air temperature affected by AHU 716 andsensed by temperature sensor 717. In the exemplary embodimentillustrated in FIG. 7, the output provided by temperature sensor 717 isprovided to feedback controller 702 as a feedback signal and is providedto fault detection module 708. Fault detection module 708 is configuredto monitor the signal(s) received from temperature sensor 717 for asignal component corresponding to the modulated damper position signalprovided to AHU 716 by extremum seeking controller 716.

Referring now to FIG. 8, a block diagram of a system 800 is shown,according to an exemplary embodiment. In system 800, extremum seekingcontroller 820 determines a performance gradient through the use of highpass filter 822, a demodulation signal provided by generator 821, and adither signal provided by generator 831. Integrator 828 is used to drivethe performance gradient to zero in order to optimize the closed loopsystem created by extremum seeking controller 820 and process system840. Process system 840 is represented mathematically as a combinationof input dynamics 842, performance map 844, and output dynamics 848.Input dynamics 842 provides a function signal u which is passed tononlinear performance map 844. The output of performance map 844 is thenpassed to output dynamics 848 to provide an output signal y_(p).Extremum seeking controller 820 seeks to find a value for u thatminimizes the output of performance map 844, thereby also minimizingoutput signal y_(p). As an illustrative example, output signal yp may berepresented by the expression:

y _(p) =p(u)=(u−u _(opt))²

where p(u) represents the performance map and u_(opt) represents thevalue at which p(u) is minimized. The actual representative format of aperformance map for any particular process system is system andapplication specific. Output signal y is passed through output dynamics848 to provide signal y_(p), which is received by extremum seekingcontroller 820. The performance gradient signal is produced byperturbing the system by adding a dither signal to the ESC loop atprocessing element 832. Return signal y_(p) (i.e., performance measure)is used to detect the performance gradient through the use of high-passfilter 822, a demodulation signal combined with (e.g., multiplied by)the output of high-pass filter 922 at processing element 924, andlow-pass filter 826. The performance gradient is a function of thedifference between u and u_(opt). The gradient signal is provided as aninput to integrator 828 to drive the gradient to zero, optimizing thecontrol loop.

While various embodiments described throughout this disclosure relate tominimizing an output signal, minimizing an error, minimizing a gradient,minimizing the performance map, and the like, it should be appreciatedthat various other optimizing systems may seek to maximize similar ordifferent values, controlled variables, or performance measures relatingto a process system.

Referring still to FIG. 8, performance measure y_(p) is provided fromprocess system 840 to fault detection module 802. Fault detection module802 is shown to include a bandpass filter 804 which is configured tofilter out low and high frequencies around the angular frequency of thedither signal so that a signal component indicative of the dither signalcan be extracted from performance measure signal y_(p). If the value vof the signal provided by bandpass filter 804 is greater than athreshold, a signal component indicative of the dither signal wassignificantly preserved by process system 840, and fault detectionmodule 802 will indicate that a fault does not exist. Conversely, if thevalue v of the signal provided by bandpass filter 804 is less than orequal to the threshold, a signal component indicative of the dithersignal was not significantly preserved by process system 840, and faultdetection module 802 will indicate that a fault exists.

Referring now to FIG. 9, a block diagram of a system 900 having anextremum seeking controller with actuator saturation control 920 isshown, according to an exemplary embodiment. Feedback from actuator 940(e.g., an actuator for an AHU damper, the element being directlyadjusted by the extremum seeking controller) has been added to system900 to limit the effects of actuator saturation. The difference betweenthe input and output signals for actuator 940 controlled by extremumseeking controller 920 is calculated at processing element 938. In anexemplary embodiment, processing element 938 computes the differencebetween the signal sent to the actuator and a measurement taken at theactuator that is indicative of the physical output of the actuator. Thedifference signal produced by processing element 938 is then amplifiedby a gain 930 and added to the input of integrator 932 at processingelement 928, thereby limiting the input to integrator 932 and preventingthe integrator from entering a condition known as “winding up.” In anexemplary embodiment, processing element 938 is implemented in software(e.g., stored in memory as code and executed by a processing circuit)and compares the signal output to the actuator to a stored range ofvalues corresponding to the physical limits of the actuator.

Referring still to FIG. 9, the difference signal produced by processingelement 938 is provided to fault detection module 902 with performancemeasure y_(p)from process system 950. Fault detection module 902includes a low pass filter 906 for removing noise from the signalreceived from element 938. Fault detection module 902 includes adecision block 908 where the output from low pass filter 902 is checkedfor an actuator saturation condition in addition to the presence of adither signal component. If the difference d between the actuator inputand the actuator output is small relative to a threshold h_(d) for theactuator saturation condition, then the actuator will be known to not besaturated. When v is smaller than the threshold h_(v) for identifyingthe presence of the signal component indicative of the dither added tothe system and the actuator is not saturated, the fault detection modulewill determine that a fault exists in the system (e.g., and that thelack of the dither signal component on the output is not simply due tothe actuator being temporarily saturated). According to an exemplaryembodiment, the difference d between the actuator input and the actuatoroutput is low-pass filtered to remove noise or other transient states ofthe difference signal.

Referring now to FIG. 10, a block diagram of a system 1000 having amulti-variable extremum seeking controller 1020 is shown, according toan exemplary embodiment. Extremum seeking controller 1020 seeks tooptimize process system inputs u₁ and u₂ to minimize the output ofperformance map 1064. In other words, extremum seeking controller 1020works to drive two performance gradients to zero by perturbing processsystem 1060 in two different ways (e.g., by modifying input signalsprovided by generator 1022 and generator 1024). According to theexemplary embodiment shown in FIG. 10, fault detection module 1002includes two bandpass filters 1004 and 1006 configured to extract thetwo modifying input signals used to perturb process system 1060 byextremum seeking controller 1020. Particularly, bandpass filter 1004 isconfigured to monitor for angular frequencies according to ω₁, theangular frequency at which generator 1022 provides its dither signal,and bandpass filter 1006 is configured to monitor for angularfrequencies according to ω₂, the angular frequency at which generator1024 provides its dither signal. Decision element 1008 checks forwhether either the output from bandpass filter 1004 or the output frombandpass filter 1006 indicates a fault in the system.

Referring now to FIG. 11, extremum seeking controller 1120 is shown toconfigured for multi-variable optimization to include m modifying inputsto process system 1160 and to seek the minimization of m performancegradients. Accordingly, system 1100 includes fault detection module 1102including bandpass filter bank 1104 for monitoring for all of the dithersignals provided by the various generators of extremum seekingcontroller 1120. Decision block 1106 checks for whether any of thebandpass filter outputs indicate a fault in the system (e.g., whetherany of the bandpass filter outputs indicates that a modifying input hasnot expectedly propagating through the system to the output of processsystem 1160).

Referring generally to the exemplary embodiments shown in FIGS. 5-11 andvarious contemplated alternatives thereof, it should be noted that anynumber of modifying inputs may be provided to the process system and anynumber of process system outputs may be present in the system and usedby the extremum seeking controller and the fault detection module toconduct the fault detection activities described herein. While some ofthe fault detection modules shown in FIGS. 5-11 utilize bandpass filtersto isolate/monitor performance measures of the system for signalcomponents indicative of the modifying signals added to the system, itshould be noted that other configurations and methods may be used. Forexample, in some exemplary embodiments, a frequency domain analysisusing, for example, a fast Fourier transform (FFT) may be used tomonitor for the signal component and to detect faulty operation. In yetother exemplary embodiments, the variation of system output can betracked using time-domain (e.g., zero-cross detection) analysis. Invarious embodiments having a bandpass filter, the bandpass filter mayhave a passband of 0.8*ω_(d)˜1.2*ω_(d). In various other embodimentshaving a bandpass filter, the bandpass filter may be a second orderButterworth filter with a passband of 0.8*ω_(d)˜3.5*ω_(d) . The passbandof 0.8*ω_(d)˜3.5*ω_(d) may account for systems in which somenonlinearity in the static map produces strong second or third harmonicsthat can be observed for fault detection purposes. Further, a variety ofadditional processing may be applied to monitored and/or filtered signalcomponents for fault detection purposes. For example, the mean averagedifference (MAD) or the standard deviation (STD) of a performancemeasure may be examined for faults. Other types of statistical analysisof the performance measure may also or alternatively be conducted todetermine if the indicia of a modifying input added to the system ispresent in the performance measure.

Referring now to FIG. 12, a flow diagram of a process 1200 for detectinga fault in a process system is shown, according to an exemplaryembodiment. Process 1200 is shown to include operating the processsystem (step 1202), which may include one or more steps for optimizingthe system. Process 1200 is further shown to include modifying an inputof the process system with a modifying signal (step 1204). In variousexemplary embodiments, modifying the input of the process system with amodifying signal in step 1204 may be a part of the one or more steps foroptimizing the system (e.g., the modifying signal may be used in theoptimization process). Process 1200 is further shown to includemonitoring an output of the process system for a signal componentcorresponding to a function of the modifying signal (step 1206). Thesignal component may be a harmonic of the modifying signal, amplitude orphase corresponding to the modifying signal, or any other indicia of themodifying signal at an output of the process system. Process 1200further includes determining that a fault in the process system existsbased on at least one of a reduction of the signal component and anunexpected transformation of the signal component (step 1208). If thesignal component is received at the process system output as expected,on the other hand, a determination may be made that no fault in thesystem exists.

Referring now to FIG. 13, a flow diagram of a process 1300 for detectinga fault in a process system is shown, according to another exemplaryembodiment. The process system of process 1300 utilizes an extremumseeking controller and process 1300 is shown to include the step ofoperating the process system according to a first input received from afirst controller and a second input received from an extremum seekingcontroller (step 1302). Process 1300 further includes modifying thesecond input with a modifying signal (step 1304). According to anexemplary embodiment, the modifying signal is a sinusoidal dither signalapplied to the process system as a part of the extremum seeking controlstrategy. Process 1300 is also shown to include monitoring a performancemeasure of the process system for an indication of the modifying signal(step 1306) and determining whether a fault in the process system existsbased on a presence, absence, reduction, or transformation of theindication (step 1308).

Referring now to FIG. 14, a block diagram of a control system 1400 foraffecting the temperature of a building space is shown, according to anexemplary embodiment. Control system 1400 includes a supervisorycontroller 1402, a controller 1404, a temperature regulation system1406, a temperature sensor 1408, an actuator 1410, and a damper 1412.Controller 1404 receives temperature setpoint information fromsupervisory controller 1402. The temperature setpoint is used to drive acontrol loop including the temperature regulation system 1406,temperature sensor 1408, and temperature regulation system controller1414. Temperature regulator system controller 1414 compares thetemperature measured by temperature sensor 1408 and received viainterface 1426 to the setpoint temperature provided by supervisorycontroller 1402 via an interface 1426. A temperature regulation commandsignal is provided to temperature regulation system 1406 via aninterface 1426. Temperature regulation system 1406 provides mechanicalheating or cooling in order to drive the temperature of the air affectedby the system to the setpoint. Controller 1404 further includes acontrol loop that controls the position of damper 1412 (e.g., outdoorair damper) via actuator 1410 and interface 1426. The control loop thatcontrols the position of damper 1412 searches for a setting for thedamper that minimizes the power consumed by temperature regulationsystem 1406. A performance gradient probe 1416 detects a differencebetween the optimal settings for damper 1412 and the current settingsfor damper 1412. In an exemplary embodiment, performance gradient probe1416 identifies a performance gradient between actual and optimalperformance of the system. Integrator 1418 is configured to minimize thegradient by producing an actuator command signal to drive actuator 1410to its optimal setting. Actuator 1410 receives the actuator commandsignal and regulates damper 1412, controlling a flow of air relating totemperature regulator system 1406.

In the exemplary embodiment illustrated in FIG. 14, controller 1404 isimplemented with a processing circuit 1420, memory 1422, and processor1424. According to an exemplary embodiment, processor 1424 and/or all orparts of processing circuit 1420 can be implemented as a general purposeprocessor, an application specific integrated circuit (ASIC), one ormore field programmable gate arrays (FPGAs), a group of processingcomponents, one or more digital signal processors, etc. Memory 1422(e.g., memory unit, memory device, storage device, etc.) may be one ormore devices for storing data and/or computer code for completing and/orfacilitating the various processes described in the present disclosure.Memory 1422 may include a volatile memory and/or a non-volatile memory.Memory 1422 may include database components, object code components,script components, and/or any other type of information structure forsupporting the various activities described in the present disclosure.According to an exemplary embodiment, memory 1422 is communicablyconnected to processor 1424 and includes computer code for executing(e.g., by processor 1424) one or more processes described herein. Memory1422 may also include various data regarding the operation of one ormore of the control loops relevant to the system (e.g., performance mapdata, historical data, behavior patterns regarding energy used to adjusta temperature to a setpoint, etc.). In an exemplary embodiment, thefunctions of controller 1404 are implemented as software within memory1422 of processing circuit 1420 and components 1414, 1416, 1418, and1420 are software modules of the system. Fault detection module 1419 maybe configured to detect faults by monitoring temperature sensor dataretrieved over a period of time for indicia of a signal component addedto the actuator command signal provided to actuator 1410.

According to the exemplary embodiments shown in at least FIGS. 5A-11,systems implementing the fault detection circuits, modules, and/ormethods described herein are closed-loop systems using feedback to makedecisions about changes to the input that drives the process system.

The construction and arrangement of the systems and methods as shown inthe various exemplary embodiments are illustrative only. Although only afew embodiments have been described in detail in this disclosure, manymodifications are possible. All such modifications are intended to beincluded within the scope of the present disclosure. The order orsequence of any process or method steps may be varied or re-sequencedaccording to alternative embodiments. Other substitutions,modifications, changes, and omissions may be made in the design,operating conditions and arrangement of the exemplary embodimentswithout departing from the scope of the present disclosure.

Embodiments within the scope of the present disclosure include programproducts comprising machine-readable media for carrying or havingmachine-executable instructions or data structures stored thereon. Suchmachine-readable media can be any available media that can be accessedby a general purpose or special purpose computer or other machine with aprocessor. By way of example, such machine-readable media can compriseRAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, magneticdisk storage or other magnetic storage devices, or any other mediumwhich can be used to carry or store desired program code in the form ofmachine-executable instructions or data structures and which can beaccessed by a general purpose or special purpose computer or othermachine with a processor. Combinations of the above are also includedwithin the scope of machine-readable media. Machine-executableinstructions comprise, for example, instructions and data which cause ageneral purpose computer, special purpose computer, or special purposeprocessing machines to perform a certain function or group of functions.

It should be noted that although the figures may show a specific orderof method steps, the order of the steps may differ from what isdepicted. Also two or more steps may be performed concurrently or withpartial concurrence. Such variations will depend on the software andhardware systems chosen and on designer choice. All such variations arewithin the scope of the disclosure. Likewise, software implementationscould be accomplished with standard programming techniques with rulebased logic and other logic to accomplish the various connection steps,processing steps, comparison steps and decision steps.

1. A fault detection system for detecting a fault in a process system, comprising: a first circuit configured to modify an input of the process system with a periodic modifying signal, wherein the first circuit is part of an extremum seeking controller and wherein the periodic modifying signal applied to the input of the process system comprises a dither signal applied to the input for probing for a performance gradient used by the extremum seeking controller to optimize the process system; and a second circuit configured to receive an output from the process system and to determine whether a fault exists based on at least one of a reduction of a signal component and an unexpected transformation of the signal component, wherein the signal component corresponds to a function of the periodic modifying signal; wherein the second circuit is configured to provide an output signal indicative of the presence of the fault to at least one of a computerized system, a memory device, a communications device, and an electronic display.
 2. A controller for detecting a fault in a process system, the controller comprising: a circuit configured to affect an input of the process system according to an extremum seeking control strategy, wherein the circuit is configured to modify the input with a periodic modifying signal as a part of the extremum seeking control strategy, wherein the circuit controls at least one manipulated variable of the process system by using the periodic modifying signal to identify a performance gradient in the process system; wherein the circuit is further configured to monitor an output of the process system for a signal component corresponding to a function of the periodic modifying signal, and wherein the circuit is further configured to determine whether the fault exists based on at least one of a reduction of the signal component and an unexpected transformation of the signal component; wherein the circuit is further configured to provide an output signal indicative of the presence of the fault to at least one of a computerized system, a memory device, a communications device, and an electronic display device.
 3. The controller of claim 2, wherein the process system comprises a temperature regulator configured to regulate temperature in response to a first control signal, and wherein the process system further comprises a damper moved by an actuator; wherein the circuit is configured to operate the actuator by providing a second control signal to the actuator, and wherein modifying the input of the process system with a periodic modifying signal comprises modifying the second control signal provided to the actuator with the periodic modifying signal.
 4. The controller of claim 3, wherein the circuit is configured to operate the actuator according to the extremum seeking control strategy.
 5. The controller of claim 2, wherein the circuit comprises: a filter configured to filter the output of the process system to extract the signal component from the output.
 6. The controller of claim 5, wherein the filter comprises a bandpass filter.
 7. The controller of claim 2, wherein the circuit is configured to compare the signal component to a threshold power level to determine whether the fault exists.
 8. The controller of claim 2, wherein the periodic modifying signal is at least one of rectangular, triangular, ellipsoidal, and sinusoidal.
 9. The controller of claim 2, wherein the circuit determining that the fault exists based on at least one of a reduction of the signal component and an unexpected transformation of the signal component comprises at least one of: (a) comparing the signal component to a threshold power level; and (b) comparing a phase of the signal component to an expected phase.
 10. The controller of claim 2, wherein the circuit monitoring the output of the process system for a signal component corresponding to a function of the periodic modifying signal comprises at least one of: (a) extracting the signal component from the output using a filter configured with a passband near that of an angular frequency component of the periodic modifying signal; (b) conducting a frequency domain analysis of the output using a fast Fourier transform; and (c) conducting a time-domain analysis of the output using a zero-cross detection method.
 11. The controller of claim 2, wherein the output is fed back to the first circuit for operating the process system as a closed-loop system.
 12. The controller of claim 2, wherein the input to the process system is provided by the circuit to the process system for operating the process system as a closed-loop system.
 13. The controller of claim 2, wherein the circuit is configured to operate the process system as a closed-loop a feedback controller according to the extremum seeking control strategy.
 14. A computerized method for detecting a fault in a process system, the method comprising: modifying an input of the process system with a periodic modifying signal; optimizing the process system utilizing the output according to an extremum seeking control strategy, wherein the modifying signal comprises a dither signal provided to the input as a part of the extremum seeking control strategy; monitoring an output of the process system for a signal component corresponding to a function of the modifying signal; and determining whether a fault exists based on at least one of a reduction of the signal component and an unexpected transformation of the signal component; providing an output representing the fault determination to at least one of an electronic display and communications electronics.
 15. The method of claim 14, wherein the dither signal is at least one of rectangular, triangular, ellipsoidal, and sinusoidal.
 16. The method of claim 14, further comprising: extracting the signal component from the output using a filter network.
 17. The method of claim 14, wherein determining that the fault exists based on at least one of a reduction of the signal component and an unexpected transformation of the signal component comprises at least one of: (a) comparing the signal component to a threshold power level; and (b) comparing a phase of the signal component to an expected phase.
 18. The method of claim 14, wherein monitoring for the output of the process system for a signal component corresponding to a function of the modifying signal comprises at least one of: (a) extracting the signal component from the output using a filter configured with a passband near that of an angular frequency component of the modifying signal; (b) conducting a frequency domain analysis of the output using a fast Fourier transform; and (c) conducting a time-domain analysis of the output using a zero-cross detection method.
 19. The method of claim 14, wherein the process system is an heating, ventilation, or air conditioning system. 